The present invention relates to organic electroluminescent (EL) devices, also known as organic light-emitting diodes (OLED) that emit color light.
In color or full-color organic electroluminescent (EL) displays (also known as organic light-emitting diode devices, or OLED devices) an array of colored pixels is provided. These pixels can include red, green, and blue color pixels (commonly referred to as RGB pixels). These pixels are precision patterned. The basic OLED device has in common an anode, a cathode, and an organic EL medium sandwiched between the anode and the cathode. The organic EL medium can consist of one or more layers of organic thin films, where one of the layers is primarily responsible for light generation or electroluminescence. This particular layer is generally referred to as the emissive layer or light-emitting layer of the organic EL medium. Other organic layers present in the organic EL medium can primarily provide charge transport functions and are referred to as either the hole-transporting layer (for hole transport) or electron-transporting layer (for electron transport). In forming the RGB pixels in a full-color OLED display panel, it is necessary to devise a method to precisely pattern the emissive layer of the organic EL medium or the entire organic EL medium.
In commonly assigned U.S. Pat. No. 5,937,272, Tang has taught a method of patterning multicolor pixels (e.g. red, green, blue subpixels) onto a thin-film-transistor (TFT) array substrate by vapor deposition of an EL material. Such EL material is deposited on a substrate in a selected pattern via the use of a donor coating on a support and an aperture mask.
The EL material transfer is preferably done under conditions of reduced oxygen and/or water, using a chamber such as Tang describes in the aforementioned patent. The use of vacuum or reduced pressure can facilitate the transfer of the EL material from the source to the substrate. The use of such conditions during transfer is also advantageous in that some EL materials are sensitive to oxygen and/or moisture. For example, tris(8-quinolinolato)-aluminum(III) (Alq), which is used in OLED devices, is known to react with water [F. Papadimitrakopoulos et al., Chem. Mater. 8, 1363 (1996)]. The use of a vacuum or low oxygen and/or water conditions during the transfer step can help reduce the failure rate of OLED devices. However, inadvertent contamination of the device by oxygen, moisture, and/or other components is possible during or between deposition steps or anytime there is an apparatus transfer or delay between steps. This can lead to reduced yields of OLED displays due to luminance quenching of the light-emitting layer by the contaminants.
It is therefore an object of the present invention to reduce the effects of contamination of an OLED device by air or other species.
This object is achieved by an organic light-emitting device with improved performance comprising:
a) an anode formed over a substrate;
b) a hole-transporting layer formed over the anode;
c) a light-emitting layer formed over the hole-transporting layer for producing light in response to hole-electron recombination;
d) a performance-enhancing layer formed over the light-emitting layer including one or more chemical reducing materials selected to improve the performance of the organic light-emitting device;
e) an electron-transporting layer formed over the performance-enhancing layer, and
f) a cathode formed over the electron-transporting layer.
It is an advantage of this invention that it can reverse the loss of luminance in an OLED device due to exposure of the OLED layers to air or due to a delay during manufacturing. It is a further advantage that an OLED device manufactured in accordance with this invention has improved operational stability.